Ok, got some work done on my 2x20w '95 JLH amp... right now i'm saving up for a custom transformer and aluminium to build the chassis (which doubles as the heatsink) arround it. What's done are all the electronics except for the power supply: the twin amp boards, a remote power on circuit (using an external signal from the preamp, a small transformer and a power relay), dual power meters using the venerable LM3915 and an relay output protection based on an article at the ESP site (which triggers on DC through the speakers and power-on & power-off thumps). Lots of lights and switches... can't wait to get this thing togheter!

Now, i started working on the preamp... i wanted the power and input switching to be digitally controlled via relays, and wondered, why not driving the volume digitally as well? I've seen two aproaches to this:

- Run the signal through a multiplexer acting as a variable voltage divider. Dirt cheap, but of course, i have my doubts about signal degradation
- Use a series of relays and resistors on ladder configuration; no signal degradation, but i'm already spending a lot on relays...
- Getting a triple-gang pot, and using a A/D converter on the third pot to drive the front volume display (i know, i know, but it *should* look neat atleast

So, any experiences with any of the above? I don't want to complicate my life any more already, but since i have the digital board already, a few more ics wouldn't kill me.

I got a update on new products from Texas instruments by Email today discribing the new Burr Brown digital volume control. The link does not seem to be working, but you may be interested in looking at this device by searching thier web site.

John,
This device probably deserves a new thread. There have been several discussions at this site about digital control of volume. This one looks very good. I've had some bad experience with Analog Devices DC-operated volume controls, but am still interested in something like this.
Looks pretty pricey ($19 CDN from Digi-Key, in stock already!), plus you need a micro to run it. Nevertheless, it may interest many DIYers. Have you (or any others out there) got any plans to try it out?

In reference to my previous post for the new TI/Burr Brown PGA3210 digital volume control IC.

I have some interest in testing this device in the future. However I have no time to devote to such a project at the present time since I’ am working hard on a all discrete version of my MOSFET class a power amp.

Since I have very little time to attack new projects right now my contribution would be limited to helping others to develop a test bed for this device when my time allows.

I HAVE STARTED A NEW THREAD ON THE PGA3210 Digital volume control. Please post all replies in regards to the PGA3210 there. Thanks.

Originally posted by alaskanaudio I got a update on new products from Texas instruments by Email today discribing the new Burr Brown digital volume control...

This one surely looks nice, but at $20 per IC plus the microcontroller... i might as well end up with the resistor/relay thing. However, i'm curious on how it would perform. Again, any feedback is appreciated!

The Arcam Alpha 10 has received good reviews for an amp in its price range. I notice that bypassing the pre-amp section of the 10 does reduce the noise floor, however the noise may not be coming from the LM1972. I suspect it's actually mainly from the MAX4051 input switches but I've never bothered putting an oscilloscope on to see. The noise is not noticeable on speakers, but is when using headphones.

Originally posted by Pete Fleming The Arcam Alpha 10 has received good reviews for an amp in its price range. I notice that bypassing the pre-amp section of the 10 does reduce the noise floor, however the noise may not be coming from the LM1972. I suspect it's actually mainly from the MAX4051 input switches but I've never bothered putting an oscilloscope on to see. The noise is not noticeable on speakers, but is when using headphones.

Yeah... well, this is why i wanted to stay away from "volume pot" IC's at first, but i have to draw a line somewhere. My input switching is controlled by relays and a rather simple digital circuit, but i want to stop using them there. I've seen some other approaches i'll be trying this week to see how they turn out (one that looks promising was mentioned on the PGA3210 thread, check http://members.tripod.de/MaikHerzog/...mp_text.html).

It possible to use other MDACs as volume controls besides the serially controlled CS3310 and LM1972. Analog Devices (audio specific - AD7111/A, AD7112/A, etc.), Maxim (MAX502?, etc.) and others make MDACs that are parallel input, so you don't have to use a microcontroller unless you want to. "Static" logic should have less digital hash floating around than a clocked microcontroller. The other option is to have the micro "go to sleep" a short time after a function is executed. I think Mark Levinson actually does this in their current preamp line.

Using the micro certainly does help if you want to have some fancy displays, though!

Pete: By the way, is there a schematic of the Arcam out there somewhere or did you just "pop the top" and mention what you saw? It's nice to see someone actually using some new and improved analog switches from Maxim. I wonder if any folks with Hafler 915 preamps ever do any mods like changing to a better analog switch.